The problem is that in order to immobilize you pretty much have to disrupt the CNS or break both front shoulders. A brown or grizzly bear with one shattered shoulder usually keeps right on going. They take amazing hits from high caliber rifles in the shoulders & take off at a dead run. On a charging bear a shoulder shot most likely will not slow it to any dergree. It would be hard to break a shoulder on a charging bear. A chest shot might kill it but the odds are very low that it would stop it in the next minute or so.